1. Field of Invention
The present invention relates generally to a dust tolerant windowless scanner and, more specifically, to a dust tolerant windowless scanner and its media scan assembly.
2. Description of the Related Art
Scanners typically include an array of optical sensor elements and a scan area (e.g., plate of glass) where an object to be imaged by the sensor elements is positioned. An optical path including, for example, lenses and mirrors, spans between the sensor elements and the scan area.
Referring to FIG. 3, a conventional scanner 300 includes a main housing 302, a glass plate 304, mirrors 306, 308, 310 and a lens 312 configured as shown. An optical path 314 of the scanner 300 begins at an object focal plane 316 at the top surface of the glass plate 304, reflects from the mirrors 306, 308, 310 as shown, and passes through the lens 312 to end at the sensor focal plane 318 (shown with a dashed line).
The scanner 300, as well as other conventional sheet fed facsimile and All-in-One products, employs the glass plate 304 for the object being scanned to reference against while the object is in the scan zone. The object to be scanned is moved over the object focal plane 316 by employing, for example, a conventional automatic document feeder (not shown).
A problem with the conventional scanner 300 is that the glass plate 304 must be positioned at or very near the object focal plane 316 in order for the glass plate 304 to fulfill its intended purpose of document support. Unfortunately, the positioning of the glass plate 304 in this manner provides locations (on both sides of the glass plate 304) very near the object focal plane 316 for dust or debris to accumulate. The scanner 300 is therefore highly sensitive to any small piece of dust or debris, resulting in streaks (typically, vertical streaks) on the scanned image in the direction of paper motion. Moreover, dust or debris on the reflecting surface of the mirror 306 may also be imaged due to its close proximity (e.g., 15 mm) to the object focal plane 316. The term xe2x80x9cdust or debrisxe2x80x9d means optical obstructions which may effect the transmission of light and includes, but is not limited to, paper dust, plastic dust, skin particles, metal particles, glass particles and fibers.
Although dust or debris on the top surface of the glass plate 304 can be easily removed, it is difficult to clean dust or debris from the inside of the scanner 300 particularly after the scanner 300 has been assembled. As a result, the scanner 300 is typically built on a xe2x80x9cclean linexe2x80x9d to lessen the number of product returns. This, of course, increases the manufacturing cost of the conventional scanner 300. Thus, a need exists for a low cost dust tolerant scanner which is less sensitive to particle contamination.
The principles of the present invention are applicable, generally, to a dust tolerant windowless scanner and its media scan assembly. According to the present invention, the scanner is windowless (or xe2x80x9copenxe2x80x9d), thus preventing dust or debris from accumulating at or near the object focal plane. Additionally, any dust or debris collecting surface, e.g., a mirror, along the optical path of the scanner is positioned as far from the object focal plane as possible.
In an exemplary preferred embodiment, by positioning the internal mirrors as far from the object focal plane as possible and removing the glass plate from the scanner entirely, dust or debris no longer has a surface to attach itself on or near the object focal plane. The scanner of the present invention is less sensitive to particle contamination and eliminates vertical streaks caused by dust or debris at or near the object focal plane, resulting in significantly improved scan quality.
The dust and debris tolerant scanner design of the present invention also provides manufacturing advantages. For example, the scanner of the present invention can be built in a non-clean room environment which reduces manufacturing overhead. Additionally, the scanner of the present invention eliminates parts from the assembly such as the glass plate, adhesives for the glass plate and any dust covers.
The media scan assembly for the dust tolerant windowless scanner includes upper and lower document feeder portions which define a media path adjacent to a reference surface of the upper portion. The lower document feeder portion includes a media conformance member which positions pieces of media against the reference surface as the pieces of media are advanced along the media path. The media conformance member includes ramp portions and an aperture which provides an optical path between the object focal plane within the media scan assembly and the sensor focal plane within the scanner.
A dust tolerant scanner in accordance with one embodiment of the present invention includes a housing, a document feeder mechanically coupled to the housing, and a media conformance member. The housing includes optics which define an optical path between an object focal plane and a sensor focal plane. The document feeder includes a reference surface positioned adjacent to the object focal plane, provides a media path through the object focal plane, and is configured to advance media along the media path. The media conformance member is mechanically coupled to the housing and positioned adjacent the reference surface. The media conformance member includes an aperture through which the optical path extends and is formed such that media advanced by the document feeder along the media path is biased toward the reference surface.
A media scan assembly for a dust tolerant scanner in accordance with another embodiment of the present invention includes: an upper document feeder portion and a lower document feeder portion providing a media path, the upper document feeder portion including a reference surface adjacent the media path, the lower document feeder portion including an aperture facing the reference surface, the lower document feeder portion being configured to be attached to a main housing of the scanner; and at least one drive roller configured to advance media along the media path.
A media scan assembly for a dust tolerant scanner in accordance with another embodiment of the present invention includes: an upper document feeder portion and a lower document feeder portion defining a media path, the lower document feeder portion including a media conformance member shaped to push a piece of media against the upper document feeder portion, the media conformance member including an aperture shaped to provide an optical path to the media path; and a media driver configured to reposition media along the media path.
A media scan assembly for a dust tolerant scanner in accordance with another embodiment of the present invention includes: an upper document feeder portion and a lower document feeder portion defining a media path, the upper document feeder portion and the lower document feeder portion being configured to advance media along the media path, the upper document feeder portion including a reference surface, the lower document feeder portion including an aperture facing the reference surface, the media path being configured to push a piece of media in the media path against the reference surface, the aperture providing an optical path to the media path.